The present invention is in the field of video systems. More particularly, the present invention relates to various methods of visually testing video systems for degradation of video signals that pass through video systems, as well as methods of compensating for this degradation.
Video systems may include a variety of video sources, including but not limited to computers, video cassette recorders, video cameras, and a variety of display devices, including but not limited to CRT monitors, CRT projectors, LCD projectors, DLP projectors, or other video display devices. The video sources can generate video signals of many types, including but not limited to NTSC, PAL, SECAM, as well as the types produced by computers, such as composite, monochrome analog, RGB, RGBS, RGBHV, RGsB, RsGsBs, and any additional video standards developed by IBM for personal computer compatible technology, including but not limited to CGA, EGA, VGA, SVGA, and XVGA type signals and any other standards developed by industry associations like VESA.
Regardless of the specific types of video signals produced, video signals frequently require processing and manipulation before they reach video display devices. To this end, video switchers, video distribution amplifiers, fiber-optic transmitters, fiber-optic receivers, RF-modulators and demodulators and other equipment, as well as various types of interconnecting cables, are frequently installed between video signal sources and video display devices.
Those ordinarily skilled in the pertinent arts will recognize that after video signals pass through such video system and reach video display devices, the quality of the video signals frequently degrade. The degree and type of degradation of a video signal depends upon the characteristics of components of the circuits through which the video signal is passing. The number and the individual characteristics of these components, as well as the characteristics and length of interconnecting cables used to connect them together determine the video signal degradation level.
Conventionally, in order to determine degradation level of a video signal a subjective judgment is often employed. An individual would look at an image and estimate the quality of the video signal by the way the image appears on the screen. Based on such observations, the individual would draw a conclusion regarding the performance of the video system. Obviously, in this situation the objective quality of the performance of the video system can not be properly determined because it strongly depends on the ability of the individual to make a proper visual assessment.
Alternatively, one can employ network analyzers that test video systems by measuring various video bandwidth characteristics which relate to attenuation or gain of video signals at different frequencies. However, those skilled in the pertinent arts will recognize that network analyzers, aside from being expensive, also require close proximity between video signal sources and video display devices, which in many cases is not possible. Additionally, specially trained personnel who are often in short supply and expensive are required to operate complex network analyzers.
Yet another method is available by utilizing a "split screen comparison" in which a reference video signal (the video signal that has not passed through the video system) and a degraded video signal (the video signal that has passed through the video system) are displayed side by side on different portions of the screen of the video display device. Based on the observations of the two images, one would make a comparison and draw a conclusion regarding the performance of the video system. Although this method is better then the two previous methods, the accuracy of such comparison strongly depends on the quality of the video display device used for the comparison. For example, if the video system is designed to have a 300 MHz video signal bandwidth, but the video display device has specification of only 100 MHz video signal bandwidth, there will be no possible way of observing degradation of video signals above 100 MHz.
There is also a method of evaluating performance of a video system by comparing the quality of an original video signal with a degraded video signal by using two similar display devices. However, this method also depends on the quality of the display devices in order to make an accurate determination regarding the video system performance. Moreover, both displays should be in close proximity so that both images can be readily compared. In many situations this is not possible since an input of a video system may be located 200-300 feet away from an output of the video system.
Accordingly, a clear need exists for an inexpensive and simple method of evaluating performance of video systems for degradation of video signals, as well as compensating for the degradation of the video signals that pass through video systems, in order to provide the highest quality image possible while making this measurement independent of the quality or performance of the display device.